Backscatter RFID sensor with a bend transducer

1. A system for sensing bending of a monitored object, comprising: a radio frequency (RF) reader transmitting a read signal and, in response, receiving a reflected signal; and a wireless bend sensor including an antenna, a chip electrically connected to the antenna, and a bend transducer electrically connected to the chip, wherein the antenna receives the read signal and reflects the reflected signal and wherein the reflected signal is modulated based on a bend radius of the bend transducer, wherein the RF reader further comprises a bend determination module determining a value of the bend radius based on a difference between the reflected signal when the wireless bend sensor is in an absorbing state and when the wireless bend sensor is in a reflecting state.

2. The system of claim 1 , wherein the read signal has a frequency in the range of 5 to 5.8 GHz.

3. A system for sensing bending of a monitored object, comprising: a radio frequency (RF) reader transmitting a read signal and, in response, receiving a reflected signal; and a wireless bend sensor including an antenna, a chip electrically connected to the antenna, and a bend transducer electrically connected to the chip, wherein the antenna receives the read signal and reflects the reflected signal and wherein the reflected signal is modulated based on a bend radius of the bend transducer, wherein the bend transducer comprises a microwave structure coupled to the monitored object and being deformed with movement of the object to vary the bend radius.

4. The system of claim 3 , wherein the read signal has a frequency in the range of 902 to 928 MHz, in the range of 2400 to 2483.5 MHz, or in the range of 5825 to 5850 MHz.

5. The system of claim 4 , wherein the bend transducer comprises a transducer formed from liquid metals.

6. A system for sensing bending of a monitored object, comprising: a radio frequency (RF) reader transmitting a read signal and, in response, receiving a reflected signal; and a wireless bend sensor including an antenna, a chip electrically connected to the antenna, and a bend transducer electrically connected to the chip, wherein the antenna receives the read signal and reflects the reflected signal, wherein the reflected signal is modulated based on a bend radius of the bend transducer, wherein the bend transducer is configured to have differing impedances Corresponding to a plurality of values or the bend radius, wherein the RF reader comprises memory storing a set of values of the bend radius and,for each of the bend radius values in the set, a signal parameter, and wherein the RF reader comprises a bend determination module processing the reflected signal to determine a reflected signal parameter and to determine an amount of bend of the monitored object by comparing the determined parameter of the reflected signal with the stored signal parameters.

7. The system of claim 6 , wherein the signal parameters comprise at least one of phase and amplitude.

8. A system for sensing bending of a monitored object, comprising: a radio frequency (RF) reader transmitting a read signal and, in response, receiving a reflected signal; and a wireless bend sensor including an antenna, a chip electrically connected to the antenna, and a bend transducer electrically connected to the chip, wherein the antenna receives the read signal and reflects the reflected signal and wherein the reflected signal is modulated based on a bend radius of the bend transducer, wherein the bend transducer is linked to the chip to define a reflecting impedance of the chip, whereby the reflecting impedance of the chip varies with the bend radius of the bend transducer.

9. A system for sensing bending of a monitored object, comprising: a radio frequency (RF) reader transmitting a read signal and, in response, receiving a reflected signal; and a wireless bend sensor including an antenna, a chip electrically connected to the antenna, and a bend transducer electrically connected to the chip, wherein the antenna receives the read signal and reflects the reflected signal and wherein the reflected signal is modulated based on a bend radius of the bend transducer, wherein the bend transducer is spaced a distance apart from the chip and the antenna, whereby the bend transducer is deformed independently from any deforming of the antenna.

10. A bend sensor, comprising: an RF antenna; an integrated circuit linked to the RF antenna, wherein the integrated circuit is semi-passive and, in response to a read signal received by the RF antenna, operates the RF antenna to transmit a reflected signal; and a transducer linked to the integrated circuit to define a reflecting impedance of the integrated circuit defining amplitude and phase of the reflected signal, wherein the transducer has an impendance varying with an amount of deformation of the transducer.

11. The bend sensor of claim 10 , wherein the transducer comprises a passive tag with a charge pump connected in series to an absorbing impedance element or included in the absorbing impedance element.

12. The bend sensor of claim 10 , wherein the transducer comprises a passive tag with a charge pump connected in parallel to both an absorbing impedance element and the reflecting impedance of the integrated circuit.

13. The bend sensor of claim 10 , wherein the transducer comprises an upper conductor and the amount of the deformation is defined by a bend radius of the upper conductor.

14. The bend sensor of claim 10 , wherein the transducer comprises a substrate that is planar in a non-deformed state and wherein the substrate is spaced apart from the integrated circuit, whereby the substrate is independently deformable relative to the integrated circuit and the antenna.

15. The bend sensor of claim 10 , further comprising a switch switching impedance of the integrated circuit between an absorbing impedance and the reflecting impedance, whereby the reflected signal is alternately defined by the absorbing and reflecting impedances.

16. The bend sensor of claim 10 , wherein the read signal is at a frequency greater than 5 GHz and the antenna and the transducer are microwave structures.

17. The bend sensor of claim 10 , wherein the transducer comprises a transmission element comprising a planar strip of copper mounted on a flexible substrate made up of a dielectric layer and an electrically conductive ground layer.

18. A wireless bend sensing assembly, comprising: an RFID tag comprising an antenna, a chip, and a transducer, wherein the transducer is connected to the chip to define reflecting impedance of the chip and wherein the transducer is adapted to have an input impedance varying with a bend radius of the transducer; and an RF reader transmitting a read signal to the RFID tag and receiving a reflected signal from the antenna of the RFID tag, the reflected signal having parameters varying with changes in the bend radius of the transducer.

19. The assembly of claim 18 , wherein the varying parameters include phase and amplitude.

20. The assembly of claim 18 , wherein the transducer has differing input impedances corresponding to a plurality of values of the bend radius, wherein the RF reader accesses memory storing a set of the values of the bend radius and, for each of the bend radius values in the set, a signal parameter, and wherein the RF reader comprises a bend determination module processing the reflected signal to determine a reflected signal parameter and to determine an amount of bend of the transducer based on the determined parameter of the reflected signal and the stored signal parameters.

21. The assembly of claim 18 , wherein the read signal is transmitted at a frequency of about 5.8 GHz.

22. The assembly of claim 18 , wherein the transducer comprises a flexible substrate supporting a flexible microwave structure adapted to vary in impedance with changes to the bend radius and wherein the supporting substrate is spaced apart from the antenna, whereby the bend radius is varied free of deformation of the antenna.